1. Field of the Invention
The present invention relates to a process for the preparation of beads comprising a solid crosslinked inorganic matrix and to the beads obtained.
2. Description of the Related Art
Materials composed of silica particles are used in many fields, for example in the medical field or in the cosmetics industry. When the particles have sizes of the order of a micron, they constitute pulverulent materials which are difficult to handle. Particles of the order of a millimeter do not exhibit these disadvantages and various processes for their manufacture have been developed.
One of these processes consists in preparing a suspension comprising a preprepared oxide powder and an organic binder, in forming (for example by extrusion), in then consolidating by a heat treatment and in optionally depositing an active phase in the pores. Such a process involves specific equipment in order to provide for the forming and the geometry of the particles thus formed. Another process consists in preparing an aqueous suspension comprising an oxide powder and a binder and in then adding this suspension to an oil in order to produce a microemulsion of aqueous droplets which comprise an inorganic phase which crosslinks. However, by this process, only beads with a size of the order of a micron, of between 0.1 and 100 microns, can be obtained.
U.S. Pat. No. 4,063,856 discloses a process for the production of beads of an inorganic material which consists in dissolving in water an organic binder, for example an alginate, capable of gelling in the presence of a divalent or trivalent cation salt (for example a calcium salt), in suspending in said solution the precursors of the inorganic material forming the beads and in then introducing this suspension dropwise into a solution of said divalent or trivalent salt. In addition, U.S. Pat. No. 4,797,358 discloses a process for the preparation of silica grains comprising a microorganism or an enzyme. The process consists in preparing an aqueous mixture comprising the microorganism or the enzyme, an alginate and a silica salt and in then adding this mixture to an aqueous solution of a polyvalent cation salt (calcium chloride, aluminum chloride, calcium acetate, aluminum sulfate) in order to obtain gelled grains. The beads thus obtained are soft beads. In the process of these two documents, the silica added constitutes a simple inorganic filler dispersed within the gelled alginate matrix and does not in any way form a crosslinked solid matrix.
The aim of the present invention is to provide a process for the preparation of beads having a crosslinked inorganic matrix with a size controlled in the millimeter range, and also the beads obtained.